Skin
cancer is a significant public health issue in Australia. Exposure to
ultraviolet radiation emitted by the sun in the UVA and UVB wavelengths is the primary
cause. Australia has been a world leader in efforts to protect the ozone
layer, the main line of defense against ultraviolet radiation emitted by the
sun. Ultraviolet radiation induces the formation of thymine dimers that cause
mutation of skin cells if not repaired before DNA replication. Mutations of
tumor suppressor genes can lead to uncontrolled cell growth. Ultraviolet radiation
also causes immunosuppresion that allows skin cancers to become established.
Basal cell carcinoma, squamous cell carcinoma, and melanoma are types of skin
cancer caused by sun exposure, though each form is associated with a different
pattern of exposure. Australia has the highest rate of skin cancer in the
world, due to a combination of tropical latitude, fair-skinned population,
outdoor lifestyle, and high amount of ambient ultraviolet radiation.
Widespread opinions about tanning and health benefits of sunlight lead many
Australians to intentionally overexpose themselves to the sun. State cancer
councils have developed sun safety and awareness campaigns, such as “Slip!
Slop! Slap!” and “SunSmart,” to educate the population about sun exposure and
encourage early detection of skin cancers. Gradual changes in knowledge and
behavior indicate that the fight against skin cancer can be won.

Introduction

Australia has the
highest rate of skin cancer in the world. The combination of the predominantly
light-skinned population, tropical latitude, and cultural emphasis on out-door
activities have contributed to this problem. The Australian government has
taken measures to educate the public, reduce skin cancer rates, and advocate
early cancer detection. Australia is also active in global efforts to reduce
destruction of the ozone layer, the main protection against the ultraviolet radiation
that causes skin cancer. Numerous studies have been conducted in Australia on
many aspects of skin cancer including those on the molecular biology of the
cancer cells, ultraviolet-induced mutagenesis, social and behavioral aspects of
skin cancer risk, and the effectiveness of government programs to combat
cancer.

Ultraviolet Radiation and the Ozone Layer

Ultraviolet
radiation is divided into three types based on wavelength. UVA radiation is
the longest wavelength, 315-400 nm, and is just slightly shorter than visible
light. UVB is radiation of wavelength 280-315 nm. UVC, the highest energy
radiation, has wavelength below 280nm (de Gruijl 1999). Each of these forms of
ultraviolet radiation is harmful to living cells.

The primary line
of defense against harmful ultraviolet radiation is the ozone layer in the
stratosphere, 15 to 30 km above the surface of the earth (Australian Government
Department of the Environment and Heritage 2003). Approximately 2 billion
years ago, molecular oxygen produced by early life on earth began to increase
the atmospheric O2 content. Molecular oxygen in the upper
atmosphere absorbs short-wave UVC radiation and decomposes to form singlet
oxygen, O. When these O atoms encounter molecular oxygen (O2)
molecules, they react to form ozone, O3. The O3
molecules absorb UVB radiation up to about 310 nm in wavelength. The ozone
layer screens out all of the UVC and much of the UVB radiation emitted by the
sun, protecting life on earth from these high-energy wavelengths (de Gruijl
1999).

The ozone layer
plays a critical role in the battle against skin cancer by blocking out much of
the ultraviolet radiation from the sun. Any increase in the amount of UVB
reaching the earth has a significant impact on human health. Studies on the
mathematical relationship between the ozone layer, ultraviolet radiation, and
skin cancer incidence estimate that a 1% reduction in ozone concentration will
increase UVB radiation exposure by 2%. This will cause an increase in the
incidence of non-melanoma skin cancers of between 3% and 6%, and an increase in
the incidence of melanoma by between 1% and 1.5% (Kripke 1988).

This increase in
skin cancer incidence is a delayed effect. A patterned increase in skin cancer
occurrence takes several decades to develop, and measurable decreases in ozone
concentration have been reported for approximately thirty years. Adults with
skin cancer twenty years ago were not likely impacted by the increase in UVB
exposure as children. Therefore, ozone depletion was probably not the cause of
the initial increase in skin cancer incidence reported ten to twenty years ago
(Kripke 1988). The impact of ozone depletion on the occurrence of skin cancer
will become more apparent as those born the last thirty years reach adulthood.

Ozone Protection in Australia

The
ozone layer has been depleted in recent decades by the use of substances that
upset the balance of chemical reactions taking place in the stratosphere. These
substances include chlorofluorocarbons, halons, methyl chloroform, carbon
tetrachloride, hydrochlorofluorocarbons, and methyl bromide. They are used in
a variety of ways in refrigeration, dry cleaning, solvents, and fire
extinguishers. There has been a 5% to 9% depletion of the ozone layer over Australia
since the 1960s (Australian Government Department of the Environment and
Heritage 2003).

Australia
has been a world leader in efforts to protect the ozone layer. In 1994, The
Australian and New Zealand Environment and Conservation Council banned the
production of halons. A ban on chlorofluorocarbons followed in 1996, as well
as controls to phase out hydrochlorofluorocarbons. Numerous ozone protection
acts are also in place on the state level in Australia (Environment Protection
Authority 2003).

In addition to
enacting state and national level legislation regulating ozone-depleting
compounds, Australia was a major player in the development of the Montreal
Protocol, the first international cooperative effort to protect the global
environment. The original Montreal Protocol was signed in 1987 and set
measures for worldwide control of the production and use of substances that
damage the ozone layer. It has been revised eight times since then to reflect
advances in technology. These advances allow more environmentally friendly
practices to replace ozone damaging activities more quickly than originally
planned. Australia makes annual contributions toward the Montreal Protocol and
also spends AUS$4.2 million each year to help developing nations reduce their
dependence on ozone-depleting substances (Environment Protection Authority
2003).

Types of Skin Cancer and Sun Exposure

The three most
common forms of skin cancer are Squamous Cell Carcinoma (SCC), Basal Cell
Carcinoma (BCC), and melanoma. Ultraviolet exposure patterns are specific to
the development of each type of skin cancer, and each type has its own
pathological characteristics.

SCC is related to total lifetime sun exposure and a pattern of continuous
exposure (Armstrong and Kricker 2001). Damage accumulated over time results in
tumors on highly exposed skin, such the face, neck, and backs of the hands. SCC
is not nearly as aggressive as melanoma, but SCC tumor cells can metastasize
and become life threatening if not identified and treated early (de Gruijl
1999).

BCC is the most
common of the three types of skin cancer. It is correlated with accumulated
exposure, but is more strongly associated with the number of sunburn episodes
over the course of a lifetime, particularly childhood sunburns. This is a
pattern of intermittent exposure (Armstrong and Kricker 2001). BCC tumors
occur on commonly exposed skin, usually on the head. Regularly highly exposed
areas like the backs of the hands are rarely affected by BCC, but the occasionally
sunburned regions like the trunk are more often affected. It grows invasively
but is less likely to metastasize than SCC or melanoma tumors (de Gruijl 1999).

Melanoma is the
least common but most deadly form of skin cancer. It grows very aggressively
and metastasizes rapidly. Melanoma is not linked to accumulated ultraviolet
radiation exposure. It is strongly correlated with infrequent severe sunburns,
especially those during childhood. Melanoma’s association with intermittent
sun exposure patterns is even stronger than that of BCC (Armstrong and Kricker
2001). Though melanoma often occurs on highly exposed parts of the body, it is
distributed more widely than either SCC or BCC (English et al. 1997).

Molecular Causes of Skin Cancer

The overwhelming
majority of skin cancer cases are caused by exposure to ultraviolet light. Ultraviolet
radiation, especially UVB, is absorbed by DNA. Absorption causes neighboring
pyrimidine bases to form either cyclobutane dimers or 6-4 photoproduct dimers.
Dimerization changes the base-pairing properties of the DNA strands. If the
dimers are not excised and replaced with normal bases before DNA is replicated,
the daughter cells may carry mutations at those sites (English et al. 1997). These mutations lead to skin cancer when
they affect tumor-suppressor genes such as TP53 in SCC and BCC cells and the
INK4A gene in melanomas (Armstrong and Kricker 2001). Loss of tumor-suppressor
genes allows the uncontrolled cell growth and division that causes tumor
formation.

UVA radiation is
much more abundant that UVB. Though UVB is much more effective at causing
sunburns, UVA radiation contributes to the formation of skin cancer by
suppressing the immune system. Ultraviolet radiation exposure disables the
Langerhans cells that take up foreign substances, process antigens, and present
them to T-lymphocytes for recognition. This immunosuppression spreads far
beyond the exposed skin and may play a role in the growth of melanomas on unexposed
sites (Kripke 1988).

Once thought to be
“safe UV,” UVA radiation’s role in the development of skin cancer was
considered minor when compared to the more intensively studied effects of UVB.
However, more recent studies indicate that UVA is much more involved in immune
suppression and cancer formation than was first realized (Baron et al. 2003). The immune suppression caused by UVA is
thought to protect cells from immune reactions against irradiated skin. These
immune reactions against sun-damaged cells cause “sun allergies.” The body
avoids these unwanted reactions by decreasing the immune response after high
ultraviolet exposure, but this also allows mutated cells to grow more readily
and develop into cancers (de Gruijl 1999).

Skin Cancer in Australia

Current
information on skin cancer in Australia indicates that one in two Australians
will develop a form of skin cancer at some point in their lives. Nearly
300,000 Australians have one or more skin cancers removed in a year, totaling
over 720,000 removal operations and over $300 million in health care costs to
the Australian Federal Government. The most recent statistical reports state
that 3,866 new cases of melanoma alone were diagnosed and 910 people died of
the cancer in 1997 (Cancer Council of Victoria 2001) out of a total Australian
population of approximately 20 million people. For comparison, in the UK
(population approximately 60 million) in 1999, there were about 65,000 cases of
skin cancer reported, 6000 of which were melanomas (Cancer Research UK 2003).
These data indicate that Australians have a melanoma rate more than double that
of their British counterparts.

There are many
characteristics of the Australian population that put them at high risk for
skin cancer. The continent is mostly populated by light-skinned people of
northern European descent, the group at highest risk for skin cancer worldwide.
This population is living in a tropical to sub-tropical region of the world
with very high ambient levels of ultraviolet radiation. The popularity of
sports and other out-door recreational activities in Australia brings people
out into the sun frequently, especially during childhood. Physical ideals such
as the “healthy tan” are popular in Australia, as in the US. Possibly as a
result of heavy influence of European ancestry, many Australians are firm
advocates of the importance of getting large amounts of sunlight. However,
there is no medical evidence that a suntan improves health (Arthey and Clarke
1995).

Sun exposure is believed
to help many conditions such as rashes and neonatal jaundice. Some people
still intentionally sun infants, thinking it will help them develop a
protective tan or cause the skin to adapt to life in the tropics. Intentional
sun exposure, especially for children, greatly increases the risk for skin
cancer later in life. Despite the dangers, some health professionals still
recommend sun exposure as a treatment for a variety of health problems
(Harrison et al. 1999).

One of the biggest
problems with childhood sun exposure in Australia is concern about vitamin D
production. Vitamin D is produced in the skin when vitamin precursors are
photolysed by UVB radiation. Many adults believe that children, especially
babies, must be intentionally sunned without ultraviolet protection in order
for the body to produce the amounts of vitamin D necessary for proper calcium
absorption and healthy bone development. Studies in the late 1980s reported
that vitamin D synthesis was suppressed by sunscreen use prompted public health
messages that lack of ultraviolet exposure would cause cancer by inducing
vitamin D deficiency. However, more recent studies have argued that sunscreen
use does not contribute to vitamin D deficiency. Especially in tropical
regions of the world, such as Australia, vitamin D requirements can be met easily
without deliberate unprotected sun exposure (Marks et at. 1995).

Sun Protection Campaigns

People born in
Australia, and those who migrate to the country before age ten, are at a much
higher risk of developing skin cancer than people who arrive after age fifteen due
to the dramatic correlation between childhood sun exposure and skin cancer
risk. Therefore, it is important to emphasize the sun exposure protection
message to children and parents. Efforts to increase awareness have utilized
flyers, posters, stickers, and activity sheets. These materials are
distributed through health care providers, daycare centers, schools, scout
groups, swimming programs, libraries, sporting groups, and pharmacies. Survey
studies indicate that these efforts have improved the attitude of the public
relating to the importance of sun protection (Smith et al. 2002).

Skin protection is
now part of health education programs in more than three fourths of schools in
Australia (Arthey and Clarke 1995). Some programs also promote school policies
such as “no hat, no play” rules that require children to wear sun protection if
they will be playing in areas with little or no shade. Efforts are being made
to move school recesses and sports to times of day with lower amounts of direct
sunlight (Garvin and Eyles 2001). In addition, sun protection messages have
been included in various parts of the school curriculum such as science,
geography, personal development, and recreation (Marks 1990).

Sun safety
programs in Australia are developed by not-for-profit state councils and
agencies that combat cancer in general. In 1980, the first sun safety
campaign, “Slip! Slop! Slap!”, encouraged people to “slip on a shirt, slop on
some sunscreen, and slap on a hat.” The most recent “SunSmart” campaign also
provides statistics on skin cancer occurrence and instructions for health care
professionals. Along with campaigns aimed at the general population, specific
efforts have been made to educate groups such as out-door workers, schoolchildren,
parents, and adolescents (Garvin and Eyles 2001).

The Anti-Cancer
Council of Victoria runs the “SunSmart” campaign to change the society’s
approach to the sun. The campaign was started in 1988 with AUS$1 million from
the Victorian Health Promotion Foundation. The program seeks to reduce and
control skin cancer by changing personal attitudes and behaviors and bringing
about environmental and organizational change. Mass media advertisement
campaigns promote sun protection to a variety of population groups. Examples
of organizational changes are the accreditation of primary schools as “SunSmart
Schools”, based on the inclusion of sun safe practices and education and the adoption
of sun protection policies for outdoor staff by local government authorities.
SunSmart has also worked with public and private organizations to influence
regulations, fashion, building design, pricing of personal sun protection
products, and shade structure manufacturing (Montague et al. 2001).

Conclusion

Psychological and
social studies have indicated that sunburns and extremely dark tans are
beginning to be viewed as “unhealthy” in Australia (Arthey and Clarke 1995).
There is now clear evidence that after decades of increase, skin cancer
incidence rates are beginning to plateau. Incidence rates in younger groups
are dropping, and treatment outcomes are improving due to early detection
(Montague et al. 2001). Australia’s continuing
efforts to protect the ozone layer and educate the public about sun protection
make up an ongoing and evolving success story for this important public health
issue.